1. Field of the Invention
This invention relates generally to corrective eye surgery. In particular, the present invention relates to methods for using a laser to perform corrective eye surgery.
2. Description of Related Art
It is well known that the eye receives its refracting power from several curved surfaces, each of which is separated by media with different indices of refraction. The most significant refractive surfaces in the eye are the anterior and posterior cornea and the anterior and posterior crystalline lens.
In a normal eye, that does not have any refractive errors, an emmetropic eye, the range of corneal refracting power is between 39 and 48 diopters, the range of lenticular refracting power is between 15 and 24 diopters, and the distance from the posterior corneal surface to the retina is between 22 to 26 millimeters.
The cornea, which is the transparent dome that serves as the outer window of the eye, is the primary and most powerful structure focusing light entering the eye. The cornea occupies one-sixth of the outer layer of the forward portion of the eye and is comprised, for the most part, of connective tissue with a thin, protective layer of epithelium on the surface.
PRK (Photo Refractive Keratectomy), which was introduced in 1987, was the first laser treatment to correct vision. Since then, a myriad of other correction techniques have been marketed. Some techniques have disappeared, while others have advanced.
PRK has had a resurgence of popularity mainly among surgeons who have reviewed the overall safety, predictability, and outcome results of PRK versus other procedures. PRK is very stable and can be used on certain people that no other procedure would be advisable. It is also the procedure of choice for those approaching the 50-year mark.
PRK is a laser treatment done directly on the surface of the cornea, as opposed to creating a flap, as with Lasik (Laser-Assisted Stromal In-situ Keratomileusis). Lasik complications typically have to do with flap creation or the flap healing process. Those patients at about age 50 and older experience flap healing complications at a rate of about 11% with Lasik. The surface cells tend to grow under the flap creating vision difficulties. There are no predicting factors (except age) as to whom this may affect. This 11% may face a long and frustrating process.